The Legend of Zelda: Skyward Sword Wiki Guide

Octorok

The Octorok is an octopus-like enemy that can be found in both land and sky trying to deter Link in his journey. Octoroks attack by shooting projectiles from their mouths. A well timed Shield bash will send the rock spit out of their mouths back at them. On land, Octoroks hide beneath objects for camouflage. In the sky, Octoroks can be found on the floating pieces of land and will shoot at Link while he's riding his Loftwing.

You can use the shield to knock back the Octorok's pellets. You must shake the Nunchuk at the moment of contact to send the pellet back at the creature or else risk taking shield damage. A vertical swipe of your sword will also send their pellets flying back at them. Octorok's only have 1 HP and are thus instantly killed by basically anything in Link's arsenal.